The present invention relates to an improvement of such a plotter using various kinds of pens and, more particularly, to an anti-dry structure of a drawing needle pen.
In a conventional plotter used in computer graphics or the like, various kinds of felt pens, ball-point pens, or drawing needle pens are prepared in a pen socket, and one of the pens is selected and held by a pen carriage so as to perform drafting. Especially, in such a plotter as is used for framing in newpapers, magazines or the like, a drawing needle pen must be able to draw very thin lines of 0.1 to 0.3 mm in width.
When the drawing needle pen is exposed to air for a few minutes, even though delayed-drying ink is used, moisture evaporates from the ink through the pen tip and the ink solidifies. Due to this the pen becomes scratchy and the line thickness becomes irregular, and in the worst case, a line cannot be drawn at all. For this reason, conventionally, the tip of the drawing needle pen stored in a pen socket is inserted in a water-containing pot so as to prevent the moisture evaporation, or the drawing needle pen held by a pen carriage is subjected to preliminary drawing. In this manner, the drawing capability of a pen is visually ascertained, and then actual drawing is started. However, when the former, i.e., the conventional technique using the water-containing pot, is employed, a water droplet adheres to the pen tip and the vicinity thereto, where the drawn ink is diluted. Therefore, it is impossible to use the drawing needle pen immediately after the pen is taken from the water-containing pot. On the other hand, when the latter, i.e., the conventional technique of preliminary drawing, is employed, solidified ink at the pen tip is not always removed. Therefore, actual drawing is often delayed until the pen tip is cleaned.